A simple dual-response fluorescent probe for imaging of viscosity and ONOO- through different fluorescence signals in living cells and zebrafish

Preparation of mitochondrial targeted near-infrared ratio fluorescent probe and its dual response detection for viscosity and ONOO- and cell imaging

The changes in viscosity and the concentration of ONOO- in mitochondria can effectively reflect the physiological and pathological status of cells. Therefore, the development of effective fluorescent probes for the sensing of viscosity and the concentration of ONOO- in mitochondria has great significance. In this article, a mitochondrial targeted fluorescent probe named Mito-RP was synthesized for the dual responsive sensing of viscosity and ONOO- by introducing pyridine ring and phenylboronic acid ester structure into 4-dimethylamino-cinnamaldehyde with long conjugated chain structure as the parent material. Mito-RP exhibits 600 folds fluorescence enhancement of viscosity in the red-light channel at 700 nm, with pyridine cation as the mitochondrial anchoring group. Simultaneously, Mito-RP appears excellent selectivity towards ONOO- using boronic acid esters as response sites. A new ratio fluorescence analysis method was constructed based on the linear correlation between the emission intensity ratio of Mito-RP at 616 nm/700 nm and the concentration of ONOO-. The linear range is 0.05-33 μM and the detection limit is 9.2 nM. Meanwhile, Mito-RP successfully monitored the changes in viscosity during lipopolysaccharide induced inflammation and rapamycin induced mitochondrial autophagy in HeLa cells. In addition, Mito-RP has also achieved visual imaging of intracellular exogenous/endogenous ONOO-. These studies provide a novel method for in-depth investigation of mitochondrial function and its role in diseases.

An ESIPT-Based Fluorochromogenic Tweezer for Reversible and Portable Detection of Al3+ Ions

ESIPT-based fluorochromes are promising materials for the detection of various chemical and biological species, particularly metal cations. Herein, we have meticulously designed a prototypical ESIPT-based α-naphtholphthalein-derived "turn-on" fluorogenic tweezer, NPDM, for the selective detection and visualization of Al3⁺ in biological and environmental samples. NPDM was found to specifically interact with Al3⁺, exhibiting dual emissions, high sensitivity (50 s), large Stokes shifts (140 and 176 nm), and a low detection limit of 16.3 nM. Notably, the sensing mechanism of NPDM for Al3⁺ involves metal ion-coordination-induced fluorescence enhancement (CHEF), ESIPT "turn-on" effect as well as restricted intramolecular rotation (RIR). This mechanism is supported by Job's plot, high-resolution mass spectrometry (HRMS), proton nuclear magnetic resonance (¹H NMR) titrations, and density functional (DFT) calculations. Interestingly, the NPDM-Al3+ ensemble can function as a secondary chromo-fluorogenic tweezer for monitoring fluoride ions (F-) with a low detection limit of 34.8 nM. Thus, an advanced molecular memory device was constructed based on the fluorescence "off-on-off" strategy and its excellent sensing properties. Moreover, a portable, smartphone-assisted intelligent platform has been developed to facilitate in-field, cost-effective, and accurate detection of Al3⁺ in real environmental water samples. Significantly, NPDM was successfully employed to image intracellular Al3⁺ and F⁻ ions in HeLa cells without interference from oxidative stress. This represents the first reported smart molecular tweezer capable of detecting Al3⁺ ions generated during electroporation within living cells. Furthermore, the strategy developed here is valuable for the creation of novel, practically beneficial luminescent molecules and offers an advanced luminescent detection platform for point-of-care sensing of health-related ionic species.

Mitochondria-targeted fluorescent probes based on coumarin-hemicyanine for viscosity changes and their applications in cells and mice

As an important parameter of the cellular microenvironment, the changes in mitochondrial viscosity are closely related to various life activities. Therefore, the development of fluorescent probes for test the changes of mitochondrial viscosity has great significance. In this study, we developed two fluorescent probes for the detection of the mitochondrial viscosity changes. The probes exhibited different fluorescence intensities at different viscosity based on the twisted intramolecular charge transfer process. The characteristics of high anti-interference performance, wide pH applicability, low cytotoxicity and excellent mitochondrial targeting performance made the probes successfully used to distinguish normal cells from cancer cells, achieving visualization of viscosity changes. Furthermore, probes P1 and P2 can also be used as early diagnosis of tumors in mice and reveal the pathology of tumor development. The probes could be serve as a promising viscosity detection tool for discriminating normal cells and cancer cells in biology-related research.

A novel ultrafast and highly sensitive NIR fluorescent probe for the detection of organophosphorus pesticides in foods and biological systems

The threat posed by organophosphorus pesticides (OPS) to food safety, human health, and the ecological environment is significant, which underscoring the need for the development of new detection tools. We designed and synthesized a NIR fluorescent probe PT-CES which targets carboxylesterase (CES), for the detection of OPS based on the principle of enzyme inhibition. The PT-CES is capable of instantaneous response to CES, exhibiting excellent stability, anti-interference capability. PT-CES realizes the quantitative detection of CES and OPS. It is noteworthy that PT-CES shows excellent stable and accurate detection ability in vegetable pesticide testing. It also enables the monitoring of CES activity in cells and liver tissue. This provides a novel tool for tracking the effect of OPS on CES activity in biological systems. Furthermore, it provides a useful method for ensuring food safety and enhancing pesticide residue analysis.

Imaging of ONOO- fluctuations during drug-induced liver/kidney injury in vitro and in vivo via a dicyanoisophorone-based NIR fluorescent probe with a large Stokes shift

Current clinical indicators for assessing liver/kidney injury are functional rather than injury indicators, which may cause some delays in the diagnosis of drug-induced liver injury (DILI) and kidney injury (DIKI). Therefore, the development of noninvasive and real-time methods for the effective diagnosis of DILI/DIKI is of great benefit to their clinical management. Herein, we constructed a dicyanoisophorone-based near-infrared (NIR) fluorescent probe (PNDP). Upon the addition of ONOO-, the probe exhibits 111.4-fold fluorescence enhancement at 665 nm with a large Stokes shift of 175 nm as well as excellent selectivity, strong anti-interference capability, and a low limit of detection (118.9 nmol L-1). More significantly, the PNDP was successfully employed for the sensitive detection of ONOO- in living cells and DILI/DIKI mice models. In vitro and in vivo bioimaging experiments demonstrated that the PNDP has greater versatility and promising potential for use as a diagnostic agent for the diagnosis of drug-induced hepatotoxicity and nephrotoxicity by monitoring ONOO- fluctuations.

Facile construction of dual-response super-resolution probes for tracking organelles dynamics

Super-resolution imaging techniques, such as structured illumination microscopy (SIM), have enabled researchers to obtain nanoscale organelle-level outputs in living systems, but they impose additional stringent requirements on fluorescence probes. However, high-performance, custom-designed SIM probes that can explain underlying biological processes remain unavailable. Herein, a customizable engineering toolkit is developed for the facile assembly of SIM probes suitable for subcellular component detection. This toolkit is used to customize a fluorescent molecule, CPC (coumarin-phenylhydrazine-carboxyl), capable of simultaneously monitoring peroxynitrite (ONOO-) and polarity distribution in mitochondria and lipid droplets (LDs), respectively, through functional ON-OFF mechanisms. The customized CPC molecule demonstrated excellent imaging capabilities under SIM, enabled the successful localization of multiple organelles, and reliably tracked the distribution of different components, thus facilitating the study of the interplay between organelles. Using CPC, the physical transition of intracellular LDs is demonstrated from heterogeneity to homogeneity. This was specifically observed during ferroptosis where the polarity of the LDs increased and their morphology became more contracted. Furthermore, the loss of LDs functionality could not counteract the accumulation of ONOO- within the mitochondria, leading to the decoupling of mitochondrial LDs during ferroptosis. These results confirmed the potential mechanism of LDs dysfunction and decoupling triggered via cumulative mitochondrial oxidative stress during ferroptosis. To summarize, this toolkit will be a powerful tool for examining subtle variations among components during the interplay between different organelles, thus offering novel avenues for understanding and treating related diseases.

Novel Ultrasensitive Fluorescent Probe for Bioimaging Carboxylesterase and Detecting Pesticide Residues in Foods

Pesticide residues pose a significant threat to food safety and human health, necessitating the development of novel detection tools. Pesticides can inhibit the activity of certain biological enzymes, so enzyme inhibition is one of the methods of pesticide detection. In this study, we developed a novel near-infrared fluorescent probe named TCFCl-CES based on the tricyanofuran structure, for ultrasensitive detection of carboxylesterase (CES). TCFCl-CES exhibits strong and stable fluorescence, excellent specificity. Notably, the fluorescence intensity of TCFCl-CES shows a linear relationship with CES concentration, achieving an exceptionally low detection limit of 4.41 × 10-5 u/mL. This ultrasensitive probe can also effectively detect pesticide residues in vegetables and monitor CES activity in cells and liver tissues. TCFCl-CES stands out for its rapid and accurate detection capabilities, making it an essential tool for accurately monitoring pesticide residue. It also has great potential for tracking CES activity in biological systems. Additionally, it offers a robust solution for food safety and improving pesticide residue analysis.

Ex Tenebris Lux: Illuminating Reactive Oxygen and Nitrogen Species with Small Molecule Probes

Reactive oxygen and nitrogen species are small reactive molecules derived from elements in the air─oxygen and nitrogen. They are produced in biological systems to mediate fundamental aspects of cellular signaling but must be very tightly balanced to prevent indiscriminate damage to biological molecules. Small molecule probes can transmute the specific nature of each reactive oxygen and nitrogen species into an observable luminescent signal (or even an acoustic wave) to offer sensitive and selective imaging in living cells and whole animals. This review focuses specifically on small molecule probes for superoxide, hydrogen peroxide, hypochlorite, nitric oxide, and peroxynitrite that provide a luminescent or photoacoustic signal. Important background information on general photophysical phenomena, common probe designs, mechanisms, and imaging modalities will be provided, and then, probes for each analyte will be thoroughly evaluated. A discussion of the successes of the field will be presented, followed by recommendations for improvement and a future outlook of emerging trends. Our objectives are to provide an informative, useful, and thorough field guide to small molecule probes for reactive oxygen and nitrogen species as well as important context to compare the ecosystem of chemistries and molecular scaffolds that has manifested within the field.

Advances in fluorescent probe development for bioimaging of potential Parkinson's biomarkers

Parkinson's disease (PD) is a common neurodegenerative disease. The clinical symptoms of PD are usually related to motor symptoms, including postural instability, rigidity, bradykinesia, and resting tremors. At present, the pathology of PD is not yet clear. Therefore, revealing the underlying pathological mechanism of PD is of great significance. A variety of bioactive molecules are produced during the onset of Parkinson's, and these bioactive molecules may be a key factor in the development of Parkinson's. The emerging fluorescence imaging technology has good sensitivity and high signal-to-noise ratio, making it possible to deeply understand the pathogenesis of PD through these bioactive molecules. Currently, fluorescent probes targeting PD biomarkers are widely developed and applied. This article categorizes and summarizes fluorescent probes based on different PD biomarkers, systematically introduces their applications in the pathological process of PD, and finally briefly elaborates on the challenges and prospects of these probes. We hope that this review will provide in-depth reference insights for designing fluorescent probes, and contribute to study of the pathogenesis and clinical treatment of PD.

Dual-channel versatile molecular sensing platform for individual and successive HClO and H2S detection: Applicable in toxic alerts of environmental samples and living organisms

In this study, we have successfully developed a novel dual-response fluorescent probe, NACou, designed for the visual and quantitative detection of HClO/H2S in real water samples and liquid beverages by a thin-film sensing platform. Additionally, NACou demonstrated efficacy for sensing HClO/H2S in HeLa cells, plants and zebrafish through distinct fluorescent channels, yielding satisfactory results. NACou exhibited a multi-modal fluorescence response mechanism for detecting HClO and H2S with remarkable low detection limits of 27.8 nM and 34.4 nM, accompanied by outstanding fluorescent enhancement (209-fold and 148-fold, respectively). These advantages position NACou as a potent molecular tool for HClO and H2S sensing. The specific recognition performance of NACou towards HClO/H2S were confirmed through fluorescence spectroscopy, mass analysis and UV-vis spectroscopy. Importantly, the thin-film sensing platform with the visible fluorescence change can enable rapid assays for water quality and food safety monitoring, showcasing significant practical application value. Impressively, NACou has been employed in warning against liver injury induced by multiple drugs, allowing for the exploration of the pathogenesis and degree of drug-induced injury.

A near-infrared fluorescent probe for viscosity: Differentiating cancer cells from normal cells and dual-modal imaging in tumor mice

As a basic parameter of the intracellular microenvironment, viscosity is closely related to the development of cancer. Thus, it is necessary to utilize a sensitive tool to visualize the viscosity in tumor cells and mice, which is helpful for the diagnosis of cancer. Herein, a novel dual-modal probe (IX-V) that has a near-infrared fluorescence (NIRF) and photoacoustic (PA) response to viscosity is synthesized. In low viscosity media, the probe has no fluorescence. With the increase of viscosity, the fluorescence is produced in the near-infrared region due to the inhibition of the TICT process. At the same time, the probe shows different photoacoustic (PA) signals in different viscosity media. Most notably, the viscosity in tumor cells has been imaged successfully by the application of IX-V, and the probe can effectively distinguish cancer cells from normal cells co-cultured in one dish by the difference of fluorescence intensity. In addition, the probe has been used for dual-modal imaging (NIRF and PA) of viscosity in tumor mice, which provides a tool for exploring the relationship between viscosity and diseases. That is to say, IX-V can achieve complementary imaging effects and has great application prospects in the tumor diagnosis.

Recent advances in fluorescent probes for dual-detecting ONOO- and analytes

Although peroxynitrite (ONOO-) plays an essential role in cellular redox homeostasis, its excess ONOO- will affect the normal physiological function of cells. Therefore, real-time monitoring of changes in local ONOO- will contribute to further revealing the biological functions. Reliable and accurate detection of biogenic ONOO- will definitely benefit for disentangling its complex functions in living systems. In the past few years, more fluorescent probes have been developed to help understand and reveal cellular ONOO- changes. However, there has been no comprehensive and critical review of multifunctional fluorescent probes for cellular ONOO- and other analytes. To highlight the recent advances, this review first summarized the recent progress of multifunctional fluorescent probes since 2018, focusing on molecular structures, response mechanisms, optical properties, and biological imaging in the detection and imaging of cellular ONOO- and analytes. We classified and discussed in detail the limitations of existing multifunctional probes, and proposed new ideas to overcome these limitations. Finally, the challenges and future development trends of ONOO- fluorescence probes were discussed. We hoped this review will provide new research directions for developing of multifunctional fluorescent probes and contribute to the early diagnosis and treatment of diseases.

Near-infrared molecular sensor for visualizing and tracking ONOO- during the process of anti-tuberculosis drug-induced liver damage

Isoniazid (INH) and pyrazinamide (PZA) are both the first-line anti-tuberculosis drugs in clinical treatment. It is notable that there are serious side effects of the drugs along with upregulation of reactive nitrogen species, mainly including peripheral neuritis, gastrointestinal reactions, and acute drug-induced liver injury (DILI). Among them, DILI is the most common clinical symptom as well as the basic reason of treatment interruption, protocol change, and drug resistance. As vital reactive nitrogen species (RNS), peroxynitrite (ONOO-) has been demonstrated as a biomarker for evaluation and pre-diagnosis of drug-induced liver injury (DILI). In this work, we developed a red-emitting D-π-A type fluorescence probe DIC-NP which was based on 4'-hydroxy-4-biphenylcarbonitrile modified with dicyanoisophorone as a fluorescent reporter and diphenyl phosphinic chloride group as the reaction site for highly selective and sensitive sensing ONOO-. Probe DIC-NP displayed a low detection limit (14.9 nM) and 60-fold fluorescent enhancement at 669 nm in the sensing of ONOO-. Probe DIC-NP was successfully applied to monitor exogenous and endogenous ONOO- in living HeLa cells and zebrafish. Furthermore, we verified the toxicity of isoniazid (INH) and pyrazinamide (PZA) by taking the oxidative stress induced by APAP as a reference, and successfully imaged anti-tuberculosis drug-induced endogenous ONOO- in HepG2 cells. More importantly, we developed a series of mice models of liver injury and investigated the hepatotoxicity caused by the treatment of anti-tuberculosis drugs. At the same time, H&E of mice organs (heart, liver, spleen, lung, kidney) further confirmed the competence of probe DIC-NP for estimating the degree of drug-induced liver injury, which laid a solid foundation for medical research.

A mitochondria-targeted dual-response sensor for monitoring viscosity and peroxynitrite in living cells with distinct fluorescence signals

Viscosity and peroxynitrite (ONOO-) are two significant indicators to affect and evaluate the mitochondrial functional status, which are nearly relational with pathophysiological process in many diseases. Developing suitable analytical methods for monitoring mitochondrial viscosity changes and ONOO- is thus of great importance. In this research, a new mitochondria-targeted sensor DCVP-NO2 for the dual determination of viscosity and ONOO- was exploited based on the coumarin skeleton. DCVP-NO2 displayed a red fluorescence "turn-on" response toward viscosity along with about 30-fold intensity increase. Meanwhile, it could be used as ratiometric probe for detection of ONOO- with excellent sensitivity and extraordinary selectivity for ONOO- over other chemical and biological species. Moreover, thanks to its good photostability, low cytotoxicity and ideal mitochondrion-targeting capability, DCVP-NO2 was successfully utilized for fluorescence imaging of viscosity variations and ONOO- in mitochondria of living cells through different channels. In addition, the results of cell imaging revealed that ONOO- would lead to the increase of viscosity. Taken together, this work provides a potential molecular tool for researching biological functions and interactions of viscosity and ONOO- in mitochondria.

Dual-Channel Fluorescent Probe for Detecting Viscosity and ONOO- without Signal Crosstalk in Nonalcoholic Fatty Liver

Nonalcoholic fatty liver disease (NAFLD) is a global health issue. Peroxynitrite and liver viscosity have recently been found to be potential biomarkers of NAFLD. Therefore, it is of great significance to develop dual-response fluorescent probes for simultaneous detecting peroxynitrite and viscosity. We report herein a new probe (CQ) that can simultaneously detect peroxynitrite and viscosity at two independent fluorescent channels without signal crosstalk. CQ shows high selectivity, rapid response, good water solubility, low cytotoxicity, and mitochondrial localization properties. In particular, CQ responds sensitively to viscosity and peroxynitrite with off-on fluorescence changes at 710 and 505 nm, respectively. The wavelength gap between these two channels is more than 200 nm, ensuring that there is no signal crosstalk during detection. With this property, the probe was applied to simultaneously detect mitochondrial viscosity and peroxynitrite and image the changes of liver viscosity and peroxynitrite concentration during the pathogenesis of NAFLD. All results show that the CQ probe is a powerful tool for simultaneous detection of viscosity and peroxynitrite and provides a potential new diagnostic method for NAFLD.

A novel "dual-locked" fluorescent probe for ONOO- and viscosity enables serum-based rapid disease screening

Peroxynitrite (ONOO^-) plays important roles in the progression of important disease such as inflammation, cancer, and diabetes, which made it an attractable target for biosensor development. However, to detect ONOO^- solely is highly dependent on the sensitivity of the detection method and may be disturbed by unwillingly false-positive signal. Cellular viscosity is an important microenvironmental parameter and its abnormal changes are closely related to diseases such as diabetes and cancer. In this case, to construct a "dual-locked" molecular tool for both ONOO^- and viscosity sensing and to evaluate the performance of such strategy in disease diagnosis is of great importance. We herein firstly reported the construction of a novel "dual-locked" probe DCI-OV which showed capability for simultaneous measuring ONOO^- concentration and system viscosity with high sensitivity (LOD = 4.7 nM) and high specificity. Moreover, both exogenous and low level of endogenous ONOO^- in living cells could be detected using DCI-OV due to viscosity amplified signal. Furthermore, cancer cells and insulin-resistant cells could be easily distinguished using DCI-OV. By taking advantage of the "dual-locked" sensing strategy, a total of 85 samples of human serum were screened using DCI-OV based rapid disease screening method and it was capable of differentiated and subdivided patients into specific type of disease, indicating the great potential of application of DCI-OV into clinical related disease diagnosis.

A xanthene-based fluorescent probe for detection of peroxynitrite in living cells and zebrafish

Peroxynitrite (ONOO^-) is one of quite critical reactive oxygen species that acts critical roles in a number of diverse biological functions and pathological events. Notably, excessive ONOO^- will lead to sorts of diseases. Thus, monitoring of endogenous ONOO^- levels will be conducive to exploring the physiological activities and functions of ONOO^-. Here, a simple turn-on fluorescent probe named DMX is reported using CN bond as the ONOO^- recognition site and xanthene as the fluorophore. DMX possessed a good linear dependence with ONOO^- concentration (0-9 μM), highly sensitive detection (DL = 37 nM), and excellent selectivity towards ONOO^-. What is more, the biological experiments reveal that DMX is able to be utilized to track exogenous/endogenous ONOO^- employing confocal laser scanning microscopy. Visualization of ONOO^- in zebrafish was also successfully conducted, suggesting that DMX might be used to study ONOO^- roles in vivo. We believe that DMX will have potential for exploring the pivotal role of ONOO^- during all sorts of physiological and pathological activities.

Research Progress on Multifunctional Fluorescent Probes for Biological Imaging, Food and Environmental Detection

There has been rapid progress in the development of fast, sensitive, cheap and low-cytotoxicity micro-molecule fluorescent probes for application in various fields, including disease diagnosis, food safety and environmental safety. As an analytical tool, dual-function fluorescent probes with dual-emission responses have attracted considerable attention due to their cost-effectiveness and efficiency over single-function sensors. This review primarily describes research progress on multifunctional probes in terms of the reaction type and coordination type, as well as the general design principles of probes. The analytes include reactive oxygen species (ROS), reactive sulfur species (RSS), harmful cations and anions, etc. Multifunctional probes for food, medical and environmental applications are listed for future research. To improve the development of rapid detection methods, trends and strategies in the development of multifunctional fluorescent probes are also discussed.